Eastern Mojave Vegetation	Autecology of Desert Elkweed Frasera albomarginata S. Watson (Syn: Swertia a.) Gentianaceae in the American Southwest (Continued)
	Tom Schweich

Topics in this Article:
Introduction
Literature Review
Field Work and Methods
Results
Taxonomy
Distribution
Growth Habits
Relationships to Soils and Other Plants
Life History
Discussion
Summary
Literature Cited
Appendix A -- Field Data
Communications Received.

Portions of this paper were paper were originally presented at the 1999 Desert Research Symposium at the San Bernardino County Museum (Schweich, 1999) and at the 2017 Desert Symposium (Schweich, 2017).

Results

I first recognized Frasera albomarginata on the north face of Wild Horse Mesa in May 1993. The high density of flowering plants caught my attention and I identified the plants in field there for the first time, after walking past them many times in the previous 12 years.

Very few plants flowered in the years 1994 through 1998. In some years, there were no flowers at all, either inside or outside my plots. From my limited perspective of six years (1993 to 1999), the density of blooming F. albomarginata has never been as high as that in May 1993. While, I have no measurements of the actual density of flowering plants in 1993, subjectively the density of flowering plants in 1999 was high, but lower than the density of flowering plants in 1993.

Table 1, below, summarizes the number of F. albomarginata by date observed and growth stage.

Table 1. Summary of observations by location.
North Wild Horse Mesa
Spring Observation	Fall Observation	Stage							Total
		1	2	3	4	5	6	7
		1st Year	Dormant	Rosette	Bud	Flower	Fruit	Dead
4/30/96		61	0	1	3	0	0	0	65
	10/18/96	0	31	0	0	0	0	35	66
4/28/97		0	0	31	0	0	0	2	33
	10/3/97	1	1	17	0	0	0	11	30
3/14/98		2	0	19	0	0	0	1	22
4/29/98		8	0	19	0	0	0	0	27
5/23/98		9	0	19	0	0	0	0	28
	9/19/98	18	0	20	0	0	0	0	38
4/21/99		20	0	11	17	0	0	0	48
5/29/99		20	0	10	17	1	0	0	48
	9/26/99	11	0	18	0	0	19	0	48
4/27/2000		3	0	28	1	0	0	19	32
6/5/2000		3	0	29	0	1	0	0	33
	9/22/2000	2	0	24	0	0	0	6	26
4/24/2001		0	1	22	3	0	0	0	26
5/26/2001		0	0	23	0	3	0	0	26
	9/16/2001	0	2	14	0	0	3	7	19
4/23/2002		0	4	0	0	0	0	15	4
5/26/2003		2	4	0	0	0	0	0	6
5/25/2004		50	1	3	0	0	0	0	56
5/25/2005		40	0	54	0	0	0	3	97
6/7/2006		26	0	46	2	21	16	1	139
6/4/2007		4	0	66	0	0	0	42	112
5/28/2008		2		31				36	72
6/2/2009		3	1	16	3	8		6	40
6/2/2010		10		16				15	41
6/2/2011		20	1	16	2	5		2	46
5/28/2012		2	3	15		2	1	22	45
Pinto Mountain
Spring Observation	Fall Observation	Stage							Total
Spring Observation	Fall Observation	1st Year	Dormant	Rosette	Bud	Flower	Fruit	Dead	Total
4/30/96		15	0	13	7	0	0	0	35
	10/18/96	0	5	13	0	0	1	16	35
4/30/97		0	0	17	0	0	0	3	20
	10/4/97	0	3	2	0	0	0	13	18
3/15/98		0	2	3	0	0	0	1	6
4/29/98		0	1	3	0	0	0	0	4
5/23/98		0	0	4	0	0	0	0	4
	9/19/98	0	0	3	0	0	0	1	3
4/21/99		0	0	2	1	0	0	0	3
5/29/99		1	0	2	1	0	0	0	4
	9/26/99	3	0	2	0	0	1	0	6
4/27/2000		6	0	3	0	0	0	1	9
6/5/2000		7	0	3	0	0	0	0	10
	9/22/2000	3	0	5	0	0	0	2	8
4/24/2001		0	0	8	0	0	0	0	8
5/26/2001		0	0	8	0	0	0	0	8
	9/16/2001	0	2	3	0	0	0	3	5
4/23/2002		0	1	0	0	0	0	4	1
5/26/2003		0	0	1	0	0	0	0	1
5/25/2004		2	0	1	0	0	0	0	3
5/28/2005		1	0	2	0	1	0	0	4
6/7/2006		9	0	1	0	3	0	1	14
6/4/2007		0	1	8	0	1	0	3	13
5/28/2008		1		5				5	12
6/2/2009				4				3	7
6/2/2010		1			2	1		1	5
6/2/2011		6		1				3	10
5/28/2012			1	6					7

My plots had 100 individuals when first established. Within two years the population had plummeted to 28, less than 1/3 of the original number. In the first full year of observation, 54% of all staked individuals died. No seedlings were observed for 1 1/2 years, from April 30, 1996, until October 3, 1997. Twenty-six new seedlings were established in 1998, an El Niño year, and the population peaked at 54 plants. A small bloom in 1999 reduced the number of live plants to the present level of slightly more that 40.

Population of F. albomarginata compared to recent years' rainfall.

I analyzed recent weather records to understand whether recent rainfall could be correlated with a high density of flowering F. albomarginata. The weather data for Mitchell Caverns was used. Mitchell Caverns is 15 km southwest of Lobo Point, and 50 m lower in elevation. Total monthly rainfall and average temperature for the 52 years, from 1959 to 2011, was normalized, and transformed into a 24-month moving average. The resulting chart, at left, shows that the Spring of 1993 was preceeded by 2 years of above average rainfall, and slightly below normal termperatures. This suggests that above normal precipitation may be required for F. albomarginata to flower in the eastern Mojave. Further analysis of more recent data will be performed when more recent weather data is available. Weather data for the 1997-1998 season show that the Winter of 1997 through the end of 1998 can be charaterized as a "wet" Winter that followed the "wet" Summer. There was been a very modest increase in the number of the species and a few flowered in the 1998 season. However, the number of plants did not increase to the levels when I established the plots in 1996. Perhaps several consecutive favorable years are required for the population of the species to increase.

The very dense bloom of 1993 may have set an extraordinary amount of seed. The Spring of 1994 had above normal rainfall and perhaps many seedlings were established. In 1996, when the experimental plots were established, there could have been an unusually high number of rosettes. However, there was a dry period of less than 50% of normal precipitation for more than 18 months. This could have caused the population to fall. My speculation, therefore, is that the very dramatic decline in F. albomarginata population in 1996-1997 was caused by a combination of an unusually high population of plants whose numbers were reduced by an unusually long and severe dry period.

Population of F. albomarginata and Salvia dorrii by observation date.

The figure at left further summarizes Table 1 and shows total population at both sites by date observed. A comparison is made with the population in a nearby plot of Salvia dorrii. I established the plot in April, 1997 as part of a separate study, then realized that the plot may provide a control for F. albomarginata populations. Salvia dorrii is a common woody perennial that produces significant amounts of seed. In my gardening with Salvia dorrii I have learned that the species germinates readily, and seedlings establish quickly. Not surprisingly, the population of Salvia dorrii increased at the same time as Frasera albomarginata during the recent years of favorable weather. Since 1999, the live S. dorrii has remained constant, while the population of F. albomarginata declined due to reproduction, and then held constant.

Frasera albomarginata population.

The figure at left shows the population of F. albomarginata by date and life stage. There about five plants that have been "dormant" since the Fall of 2000, and I expect they will be judged as "dead" with the next Spring observation.

Age of Frasera albomarginata at Flowering

My data set contains data about 61 individual plants that have flowered and produced seed by the end of the 2011 growing season. A chart of the ages of plants when they flowered is shown at left. This chart shows that F. albomarginata can be a biennial as one plant flowered in the second season following germination and establishment. Fourteen plants flowered in the third season. The remaining 46 plants that flowered were 4 or more years in age. The reason I say 4 years or more is that these plants were established rosettes in my experimental plots when the plots were established. I don't really know how old they are. I think, though, that it is reasonable to assume that these plants were established after the heavy bloom of 1993. Therefore, a preliminary conclusion is that the species is a biennial at a minumum, probably grows two to seven years before flowering, but that the age of flowering is probably influenced mainly by precipitation.

One concern is that my work in the plots could be affecting germination and establishment of seedlings. I think this might be true to a small extent. My overall impression is that the density of plants is slightly less inside my plots than outside. It is also apparent that my repeated visits to the plots is having an effect on them. This is especially true in Spring 1998 when I made three visits each a month apart. By the time I made the third visit in May 1998, my footprints and the areas in which I stepped into the plots were readily visible. Since my plots are in loose rocky soil on steep slopes, repeated use rapidly yields visible alteration of the soil surface.

No individual of the species flowered from the establishment of the plots until May, 1999. On several occasions, plants formed buds and a flower stalk. F. albomarginata may form buds, Stage 4 above, but fail to flower and set seed. Of seven F. albomarginata at Pinto Mountain that formed buds in April, 1996, one successfully set seed, two failed to flower, and four were trampled by cattle. Of three F. albomarginata at North Wild Horse Mesa that formed buds in April, 1996, all three failed to flower, and were found in October, 1996 with dried buds.

Other articles:
• Field Notes: Coll. No. 149.1;
Frasera albomarginata that failed in bud.
Frasera albomarginata that failed in bid.

149.1

My examination of one F. albomarginata that budded but failed to flower showed that the caudex was still fleshy. This might imply that F. albomarginata will bud again, if it fails to flower. However, observation has showed that once a a plant buds and then fails to flower, it will die without attempting to flower again.

Of the five plants that formed buds in April 1996, and then failed to flower, none were alive in April 1997. This implies that, once a plant starts to form a flower stalk, it is committed and will die, regardless of whether it successfully flowers and produces seed.

I have also observed some local climatic effects between the two sites of Pinto Mountain and Wild Horse Mesa. In October, 1966, all 65 staked individuals of F. albomarginata were dormant at North Wild Horse Mesa, while 12 of 26 (46%) at Pinto Mountain had green leaves, i. e., stage 3, rosette. Yet when observed the next spring, April 30, 1997, approximately equal proportions of F. albomarginata were in stage 3, rosette. This could be a permanent location effect, i.e., geology or elevation or weather patterns, or a transitory location effect, i.e., an unusual summer thunderstorm.

The Summer of 1997 is generally believed to be a "wet" summer with Hurricanes Linda and Nora bringing substantial precipitation to the eastern Mojave Desert. Indeed, when I visited my plots on October 3-4, 1997, the desert was carpeted in green and many perennial shrubs were in bloom (Coleogyne ramosissima, Krameria parvifolia and Salvia dorrii). I had expected to find many F. albomarginata in rosette form. However, I was surprised to find this was not the case. Less than half of the plants were in the rosette stage. Most of the remainder were dormant (or dead). In October 1997, most of the plants in rosette stage were at North Wild Horse Mesa instead of Pinto Mountain, as shown in the table above. This is opposite of what I found in October 1996.

There was one new plant growing at North Wild Horse Mesa in October 1997. This is the first time I have definitely observed a 1st-year rosette. Since then 25 additional seedlings have appeared in the experimental plots.

This also indicates that F. albomarginata can germinate and establish in the summer season. However, by May, 1998, there were seven more seedlings at North Wild Horse Mesa, suggesting that the species most often germinates in the winter season, although it can also germinate in the summer if conditions are right.

Notes for April, 2002: Every plant in both plots was dormant. I saw one or two F. albomarginata with leaves outside my plots. Obviously, 2002 is a dry year. So far this summer, as of August 14^th, the Mid Hills RAWS has received 0.67 inches of rain. I'm guessing that no plants will have leaves at my next planned observation in early September, 2002.

Miscellaneous photos of Frasera albomarginata in experimental plots.

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Date and time this article was prepared: 12/9/2024 7:36:01 PM